1. Field of the Invention
The present invention relates to a semiconductor wafer baking apparatus and, more particularly, to a semiconductor wafer baking apparatus that can maintain uniform temperature over a semiconductor wafer and can improve a purging efficiency during baking.
2. Description of the Related Art
Generally, semiconductor devices are manufactured through processes of ion implanting, thin film deposition, diffusion, photolithography, and etching. Among these processes, photolithography is an essential part of semiconductor manufacture, allowing a desired pattern to be formed. Photolithography involves transferring a pattern from a photo mask to a photo resist (PR) coated on a substrate, using an exposure system, and etching a predetermined pattern into a material film below using the photo resist as an etch mask. In this case, the photo resist is a photo sensitive resin, and the major components of the photo resist are polymer, a solvent, and a sensitizer.
The photolithography process includes a baking process, where the substrate is heated before or after coating with the photo resist. In the baking process, an organic solvent is removed from the photo resist in the form of fumes.
The baking process generally includes four steps. The first is a pre-baking step, in which organic materials or moisture are removed from the surface of the substrate by heating the substrate before coating the photo resist onto the substrate. The second is a soft baking, immediately after coating the photo resist onto the substrate. The third is a post exposure baking, after exposing the photo resist. The last is a hard baking, after developing the photo resist.
An apparatus for performing the baking process generally includes a hot plate that heats a wafer coated with photo resist, and a chamber in which the hot plate is mounted. A purging gas, such as N2 gas, for exhausting fumes from the photo resist during baking, is supplied to the chamber. At this time, the purging gas is one of the factors that causes a temperature gradient in the chamber, which affects the critical dimensions of the semiconductor devices integrated on the wafer. The thermal stability of the baking apparatus is a factor in the baking process, so it is desirable to heat the wafer uniformly.
Therefore, there is a need to develop a baking apparatus that can minimize the effect of the purging gas on a wafer, and can exhaust fumes from the photo resist during baking.